That's something I think many folks forget, in art your have to change or else people will eventually get bored of it.

God of War is one of those games that wants to tell a story, so of course Kratos is going to change since the game isn't meant to be a saturday morning cartoon where characters are meant to be one-dimensional. Like, if they want games like that, there's always Crash Bandicoot or Call of Duty where the plot doesn't really matter that much.